Aromatic hydrocarbons, arenes, are types of hydrocarbon compounds having one or more benzene rings, and may be classified into monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs) based on the number of benzene rings. Aromatic hydrocarbons are generally present in crude petroleum, petroleum refined products (e.g., diesel, heavy oil, and gasoline), and industrial solvents, and often used as starting materials for the manufacture of pharmaceuticals, agrochemicals, explosives, and many daily use products. However, aromatic hydrocarbons have stable and hardly degradable structures with high melting and boiling points. When released, aromatic hydrocarbons easily accumulate within and can be harmful to humans and the ecological environment.
The MAHs compounds benzene, toluene, ethylbenzene, and xylene (BTEX) are some of the most common groundwater contaminants and soil contaminants. Among the BTEX compounds, benzene often receives more attention due to its reported carcinogenicity. Benzene (C6H6), the simplest MAH, is often used as a chemical solvent or for the preparation of benzene derivatives in the chemical industry. Upon entering the human body, through skin or eye contact, inhalation, or oral routes, benzene could inhibit the central nervous system (CNS) and cause symptoms such as sleepiness, dizziness, headache, nausea, etc. Long-term contact with benzene could adversely influence the formation of red blood cells, white blood cells and blood platelets, and likely cause leukemia.
Naphthalene (C10H8) is the simplest PAH, composed of two fused benzene rings, and widely used for the production of dyestuffs, resins, solvents, disinfectants, insecticides, preservatives, mothproofing agents, etc. After entering the human body, naphthalene could cause symptoms such as haemolytic anaemia, nausea, vomiting, diarrhea, jaundice, liver or kidney damage, etc.
Because the presence of benzene and/or naphthalene in the environment poses a threat to human health and causes damage to ecological environment, much effort has been made to provide effective methods for the treatment of environmental pollutants. Current methods for the treatment of environmental pollutants include solidification, removal, incineration, activated carbon adsorption, catalytic reduction, photolysis, bioremediation, etc.
Bioremediation is a technique that utilizes the biodegradative activities of microorganisms to remove environmental pollutants and recalcitrant xenobiotics. Advantages of bioremediation include its low cost, lack of toxic by-products and secondary pollution generated during the degradation of the environmental pollutants, in situ operation, etc. Therefore, bioremediation has been widely applied to the remediation of contaminated sites. Bioaugmentation, a process of adding microorganisms with biodegradative activities to contaminated environments for the purpose of degrading pollutants, is particularly well-received among bioremediation techniques. However, certain characteristics of aromatic hydrocarbons, e.g., the low water solubility and strong sorption to soil, could adversely influence their bioavailability to microorganisms capable of aromatic hydrocarbon degradation, thereby limiting the degradation rate of aromatic hydrocarbons. Accordingly, the addition of microorganisms with emulsifying activity to the aromatic hydrocarbon-contaminated environments increases desorption rates and apparent solubility of aromatic hydrocarbons in an aqueous phase, resulting in increased bioavailability and degradation rate of aromatic hydrocarbons.
In the event that indigenous microorganisms are unable to effectively scavenge aromatic hydrocarbons, bioaugmentation may be the only way to achieve bioremediation. Therefore, it has become a goal for researchers in this field to isolate and screen microorganisms suitable for bioremediation.
Many bacterial strains with emulsifying activity and/or benzene- and/or naphthalene-scavenging ability for benzene and/or naphthalene have been isolated from contaminated environments, and mostly belong to Pseudomonas spp., Pseudoxanthomonas spp., Alicycliphilus spp., Burkholderia spp., Ralstonia spp., Achromobacter spp., Hydrogenophaga spp., Rhodococcus spp., Arthrobacter spp., Alcaligenes spp., Micrococcus spp., etc. (Jeong Myeong Kim et al. (2008), Applied and Environmental Microbiology, 74:7313-7320; Shuguang Xie et al. (2011), Biodegradation, 22:71-81; R. C. John et al. (2012), Bulletin of Environmental Contamination and Toxicology, 88:1014-1019). For example, CN 103045502 A discloses a Rhodococcus erythoropolis strain T7-3 (CGMCC No. 6104) isolated from petroleum-contaminated seabed soil samples, which was found to be effective in the emulsification and/or degradation of crude petroleum and/or petroleum hydrocarbons (including benzene and xylene). The Rhodococcus erythoropolis strain T7-3 is expected to be useful in bioremediation of petroleum-contaminated area of the sea. CN 1519312 A discloses a Rhodococcus ruber strain Em CGMCC No. 0868 isolated from crude petroleum-contaminated soils, which was found to be effective in the emulsification and/or degradation of kerosene and petroleum hydrocarbons such as benzene, naphthalene, anthracene, phenanthrene, and pyrene. The Rhodococcus ruber strain Em CGMCC No. 0868 is expected to be useful in oily wastewater treatment and bioremediation of petroleum-contaminated soils.
In E. Deziel et al. (1996), Appl. Environ. Microbiol., 62:1908-1912, E. Deziel et al. isolated twenty-three PAH-degrading bacterial isolates from a sandpit that had previosuly received oil refinery wastes, wherein Pseudomonas aeruginosa 19SJ was found to be able to produce large amounts of glycolipid using naphthalene or phenanthrene as the sole substrate. Furthermore, via glycolipid production, Pseudomonas aeruginosa 19SJ exhibits emulsifying activity that could increase apparent solubility of naphthalene, resulting in enhanced naphthalene degradation and utilization, and in turn, further promotion of glycolipid production. Therefore, production of surface-active compounds by bacteria is likely a part of their strategy for growing on poorly available substrates. For these reasons, Pseudomonas aeruginosa 19SJ is expected to be useful in bioremediation of environments contaminated with benzene and/or naphthalene.
In Eun Young Lee et al. (2011), International Proceedings of Chemical, Biological & Environmental Engineering, 20:37-41, Eun Young Lee et al. isolated Pseudomonas putida AY-10 from the rhizosphere of wastewater treatment reed. Pseudomonas putida AY-10 is able to grow on mediums with benzene, toluene, ethylbenzene, or xylene as the sole carbon source, and also completely degrade benzene, toluene, ethylbenzene, and xylene. Therefore, Pseudomonas putida AY-10 is expected to be useful in bioremediation of BTEX-contaminated environments.
Despite the microorganisms described in the above prior art, the Inventors remain committed in their efforts to screen microorganisms having emulsifying activity as well as benzene- and/or naphthalene-scavenging ability for use in environmental protection. During their research efforts, the Inventors unexpectedly isolated a new bacterial isolate, Pseudomonas taoyuanensis S03, form soils contaminated with benzene and/or naphthalene. The bacterial isolate is phylogenetically different from other bacterial species of Pseudomonas that have been published, and possesses great emulsifying activity against heavy oil and diesel, as well as benzene- and/or naphthalene-scavenging ability. Therefore, the isolate is expected to be useful in the remediation of environments contaminated with crude petroleum, petroleum refined products, benzene, and/or naphthalene.